Mold for electric discharge lamp

ABSTRACT

A mold for making a tapered cylindrically-shaped glass envelope for an electric discharge lamp is described as comprising split mold halves each having one-half of a tapered cylinder with a plurality of substantially parallel grooves formed therein. The grooves of each half mold combine to form a helically-shaped channel of nonuniform pitch winding circumferentially around the tapered cylinder.

United States Patent Witting et al.

[4 1 Feb. 25, 1975 MOLD FOR ELECTRIC DISCHARGE LAMP [75] Inventors: Harald L. Witting, Burnt Hills; John O. Fielding, Ballston Lake, both of N.Y.

[73] Assignee: General Electric Company,

Schenectady, N.Y.

[22] Filed: May 1, 1974 [21] Appl. No.: 465,904

[52] US. Cl 65/360, 249/160, 313/493 [51] Int. Cl C03b 9/34 [58] Field of Search 249/160; 65/302, 357, 360;

[56] References Cited UNITED STATES PATENTS Fithian 65/357 1,859,957 5/1932 Canfield 65/302 Primary ExaminerRobert L. Lindsay, Jr. Attorney, Agent, or Firm-Jerome C. Squillaro; Joseph T. Cohen [57] ABSTRACT A mold for making a tapered cylindrically-shaped glass envelope for an electric discharge lamp is described as comprising split mold halves each having one-half of a tapered cylinder with a plurality of substantially parallel grooves formed therein. The grooves of each half mold combine to form a helically-shaped channel of nonuniform pitch winding circumferentially around the tapered cylinder.

2 Claims, 3 Drawing Figures MOLD FOR ELECTRIC DISCHARGE LAMP The present invention relates to molds for making electric discharge envelopes and more particularly to a mold for making a tapered cylindrically-shaped envelope with a helicallyshaped channel of nonuniform pitch winding circumferentially around said tapered cylinder.

The development of helically-shaped fluorescent lamps as screw-in replacements for standard incandescent lamps has been hampered for many years by the inability to produce the necessary glass structures which can be easily mass-produced by high speed machinery. For example, helical fluorescent lamps described in US. Pat. Nos. 2,491,847 and 2,501,375 to Breadner et al. each require grooved cylindrical members which fit together with close fitting tolerances in order to avoid electrical short-circuits along the discharge paths. Such close tolerances are difficult to achieve at low cost with present glass-making machincry. Additionally, since it is highly desirable to coat the cylinders separately with phosphor before assembly, the coating is likely to be damaged if the tolerances on the mating parts are too close.

It is therefore an object of this invention to provide a mold for making helically-shaped fluorescent lamps that can be easily produced with high speed machinery at reasonable cost.

It is a further object of this invention to provide a mold for making a helically-shaped fluorescent lamp which does not require close tolerances that damage phosphor coatings on mating surfaces.

Briefly, these and other objects of our invention are achieved in accord with one embodiment thereof by providing a split mold comprising first and second mold halves of a glass-molding material, each of said mold halves including a portion of a tapered cylinder with a plurality of substantially parallel grooves formed therein. The grooves of the mating half-mold sections form a helically-shaped channel of nonuniform pitch winding circumferentially around the tapered cylinder. The novel helically-shaped channel of nonuniform pitch is characterized by a pitch of substantially zero degrees where the channel intersects with a plane passing through the intersection of the mold halves and reaches a maximum pitch at approximately 90 degrees to this plane, thereby enabling easy release of a blown glass envelope from the mold.

The novel features of our invention are set forth with particularity in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a perspective view of the split mold halves for making a helically-shaped fluorescent lamp envelope in accord with one embodiment of our invention;

FIG. 2 is a plan view ofa helically-shaped outer envelope made from the mold of FIG. 1; and

FIG. 3 is a plan view of the helically-shaped outer envelope of FIG. 2 rotated through 90 degrees along its vertical axis and sealed to the mating inner envelope.

FIG. 1 illustrates split mold halves I1 and 12 useful for making a tapered cylindrically-shaped envelope for an improved electric discharge lamp. Each mold half is made of a suitable glass-molding material, such as graphite or stainless steel. The mold halves each include tapered cylindrical halves l3 and 14 with a plurality of substantially parallel grooves 15, illustrated as having a substantially semicircular cross-section. The

grooves 15 are arranged with respect to the tapered cylindrical portions so that when the mold halves 11 and 12 are mated together along a mold parting plane 16, a helically-shaped channel of nonuniform pitch is inscribed within the tapered cylindrical portions 13 and 14.

Operationally, the split mold halves II and 12 are utilized in substantially the same manner in which molds are used for making incandescent lamps, for example. That is, the mold halves are placed together along the mold parting plane 16 and molten glassis blown into the mold. The mold halves are then opened, releasing a blown glass envelope 21, similar to that illustrated in FIGS. 2 and 3. More specifically, FIG. 2 illustrates the glass envelope 21 partially broken away, as comprising a tapered cylindrical envelope having a helically-shaped channel 17 of nonuniform pitch winding circumferentially around the tapered cylindrical portion.

FIG. 2 illustrates an important feature of our invention which makes possible mass production of this unusually-shaped envelope with high speed machinery at reasonably low cost. In particular, FIG. 2 illustrates the helically-shaped channel 17 which is characterized by a helix angle or pitch which is substantially zero where the helical channel crosses the mold parting plane 16. This region of substantially zero pitch is illustrated in FIG. 2 by the numeral 22. Each revolution of the helical channel is characterized by two regions of substantially zero pitch, one at each region where the helix intersects the mold parting plane 16.

As pointed out above, the construction of the molds 11 and 12 with these regions of substantially zero pitch causes the glass blown into the mold to have a contour which is substantially perpendicular to the mold parting plane 16. Reentrant surfaces are thereby avoided and the glass envelope is readily released from the mold. FIG. 1 illustrates these regions of substantially zero pitch in the grooves 15 by the numeral 23.

FIG. 3 is a view of the glas envelope 21 illustrating the surface of the glass envelope at degrees to the parting plane 16. In this illustration the helix pitch is a maximum, being approximately 15 degrees in this illustration.

By way of example, the mold halves 11 and 12 may be fabricated by machining the desired tapered cylindrical portions in a lathe, for example, and then machining with a ball end mill, for example, the parallel grooves 15. By way of illustration, the split molds l1 and 12 may have the following dimensions: a diameter of approximately 3 inches at the lower portion thereof with a 4 degree taper, a length of approximately 6 inches, and parallel grooves 15 having a semicircular cross-section of 1 inch diameter, thereby producing a helical groove having a length of approximately 35 inches. The helical groove produced in the glass envelope 21 is useful in providing the discharge path for an electric discharge lamp such as a fluorescent lamp.

Where the envelope 21 is utilized in an electric discharge lamp, the electric discharge is confined to the region of the helically-shaped groove 17 by inserting a tapered cylinder 24 inside the glass envelope 2]. similar to that illustrated in FIG. 3. The tapered cylinder 24 advantageously has a substantially uniform taper similar to that of the envelope 21 so that the two glass members nest together in close-fitting coaxial relationship. in this way, a helically-shaped electric discharge lamp, similar so that described in concurrently filed application Ser. No. 465,901, of common assignee as the instant invention, is provided.

In summary, those skilled in the art can readily appreciate that the fabrication of helically-shaped electric discharge lamp envelopes in accord with our invention is greatly simplified. This simplification results from the use of our novel mold which eliminates the requirement for close tolerances between mating glass parts as required by the prior art. Additionally, our novel molds may be utilized with high speed machinery similar to those employed in the making of incandescent lamps, for example.

In view of the foregoing description, it will be apparent to those skilled in the art that many modifications and changes are possible without departing from the spirit and scope of our invention. Therefore, the appended claims are intended to cover all such modifications as fall within the true spirit and scope of this invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A mold for making a tapered cylindrically-shaped envelope of glass, said mold comprising first and second mold halves of a glass-molding material, said mold halves defining a mold parting plane therebetween with each of said mold halves having one half of a tapered cylindrical portion with a plurality of substantially parallel grooves formed therein, said grooves forming a helically-shaped channel of nonuniform pitch circumferentially winding around said tapered cylindrical portions, said channel of nonuniform pitch further characterized b a pitch of substantially zero degrees where said channel intersects said mold parting plane and reaches a maximum pitch at approximately degrees to said mold parting plane, thereby enabling easy release of a glass envelope from said mold.

2. The mold of claim 1 wherein said helically-shaped channel has a substantially semicircular cross-section. l l 

1. A mold for making a tapered cylindrically-shaped envelope of glass, said mold comprising first and second mold halves of a glass-molding material, said mold halves defining a mold parting plane therebetween with each of said mold halves having one half of a tapered cylindrical portion with a plurality of substantially parallel grooves formed therein, said grooves forming a helically-shaped channel of nonuniform pitch circumferentially winding around said tapered cylindrical portions, said channel of nonuniform pitch further characterized by a pitch of substantially zero degrees where said channel intersects said mold parting plane and reaches a maximum pitch at approximately 90 degrees to said mold parting plane, thereby enabling easy release of a glass envelope from said mold.
 2. The mold of claim 1 wherein said helically-shaped channel has a substantially semicircular cross-section. 